A major cause of infertility is failure of blastocyst implantation. In the intact animal it is difficult to obtain specific information concerning cellular interactions between the blastocyst and the endometrium. An in vitro model system which mimics various aspects of implantation would allow us to conduct investigations aimed at elucidating the mechanisms involved in blastocyst implantation. The objectives of this proposal are (1) to establish an in vitro model to study the intrusive mechanism of implantation, (2) to utilize morphological techniques to elucidate the mechanism(s) of cell-to-cell contact in the models, and (1) to examine trophoblast cell interactions with epithelial cells, basal lamina, type I collagen and connective tissue cells. The guinea pig will be used to establish an intrusive model of implantation since this mimics the mechanism of implantation in the human. Initially guinea pig endometrial epithelial cells and decidualized connective tissue cells will be isolated, grown in culture, and characterized to verify their cellular origin. Then decidual cells will be mixed at appropriate concentrations with solubilized type I collagen and the mixture allowed to polymerize into pads. Guinea pig endometrial epithelial cells will be presented to the surface of the pad and allowed to form a complete monolayer. Guinea pig blastocysts will then be added and allowed to interact in the system. Morphological and immunocytochemical techniques will be used to compare and contrast the specific cellular interactions which take place. Particular attention will be given to the interaction of trophoblast cells with epithelial cells, basal lamina components, tYpe I collagen, and the decidualized stromal cells. These studies will add to our knowledge of the in vitro cellular interactions occurring in during intrusive implantation which mimics implantation in the human. The proposed model will be the first to combine the various maternal and embryonic elements involved in the initial aspects of intrusive implantation and will allow detailed examination of the cellular interactions that occur.